1. Technical Field
The present invention relates to an insulation failure diagnosis apparatus and a method of diagnosing insulation failure which diagnose presence or absence of insulation failure between a body of a vehicle and a connection path to a power supply for a traction unit installed in the vehicle.
2. Related Art
This type of insulation failure diagnosis apparatus is disclosed in, for example, Japanese Patent No. 4027727. When using this apparatus, the body of a vehicle is connected to one terminal of a power supply of a motor used as a traction unit via a capacitor and a resistor. The apparatus diagnoses presence or absence of insulation failure between the motor and the ground on the basis of a current passing through the capacitor when generating an AC voltage signal using an inverter connected to the motor.
Recently, some inverters for in-vehicle auxiliary units have been directly connected to a power supply for a traction unit. However, if the number of members connected to the power supply increases, stray capacitance between the power supply and the body of the so vehicle increases, or the value of dielectric resistance decreases. Hence, it is a concern that impedance associated with the stray capacitance or dielectric resistance is lowered. In this case, the accuracy of diagnosing the insulation failure can be lowered.